This invention relates to a rear hub for a bicycle, which is provided with an inner member fixed to a hub shell having at both axial ends thereof a pair of hub flanges, the inner member unidirectionally rotatably supporting an outer member having at least one sprocket.
Generally, this kind of rear hub has an inner member mounted on one axial end of the hub shell axially outwardly fron one of the hub flanges. The outer member having the sprocket is mounted to surround the inner member so as to be freely rotatable therewith. Ratchet teeth are provided at the inner periphery of the outer member, and pawls engageable with the ratchet teeth are supported on the outer periphery of the inner member, so that the ratchet teeth and pawls comprise a unidirectionally rotary transmission which allows the outer member to unidirectionally freely rotate.
Conventionally, the pawls supported on the outer periphery of the inner member are accommodated in chambers formed by recessing the outer periphery of the inner member. The cutting work required to form the recesses is troublesome when leads to complicated machining of the inner member. As a result, the hub is expensive to produce.
In the light of the aforesaid problem, this invention has been designed. An object of the invention is to provide a rear hub having easily machined pawl accommodating chambers to considerably decrease its manufacturing cost.
This invention is characterized in that a hub shell having a pair of first and second hub flanges is provided with a tubular extension extending axially outwardly of the first hub flange, an inner member is sleeved onto the extension and fixed thereto, and a plurality of through bores are formed at an axially intermediate portion of the inner member, so that the pawl accommodating chambers are formed with the through bores and the outer periphery of the extension.
The present invention has been designed around the fact that a pressing operation for making the through bores is simpler than the conventional cutting work for recessing the outer periphery of the inner member. The invention is so constructed that the inner member is made tubular and has the through bores, and the tubular extension is formed at the hub shell and is used, together with the through bores, to form the pawl accommodating chambers. Hence, the invention overcomes the problem associated with the conventional rear hub of having the pawl accommodating chambers formed by complicated and expensive cutting work.
In the rear hub of the invention, the inner member, which is sleeved onto the extension and reinforced therewith, can be formed of relatively thin pipe material, thereby facilitating the formation of the through bores. Also, an inner member integral with first hub flange can be formed by use of one metallic plate in a constriction process. As a result, the rear hub of the invention is even less expensive to produce.
These and other objects and novel features of the invention will be more apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.